In oil and gas operations, stimulation or treatment of the subterranean formations using a fluid containing suspended particles, referred to as hydraulic fracturing, may be used to improve production. That is, a fluid, referred to in the art as a fracturing fluid, is pumped or injected through a well bore into a subterranean formation to be stimulated at a rate and pressure such that existing fractures are opened and/or new fractures are formed and extended into the subterranean formation. The fracturing fluid carries particles, referred to in the art as proppant particles, into the fractures. The particles are deposited in the fractures and the fracturing fluid dissipates into the subterranean formation and/or is returned to the surface. The particles function to “prop” open or prevent the fractures from closing whereby conductive channels remain through which produced fluids can flow to the well bore.
The paper “Propping Fractures with Aluminum Particles”, Kern L. R. in (Petroleum Technology, June 1961 p. 583) teaches the use of malleable aluminum particles for producing high-conductivity fractures. Kern also teaches that flow capacity may be increased several fold with a sparse distribution of particles, but such flow capacity is limited by both crushing of the propping particles and by embedment of the propping particles in the walls of the formation. Kern teaches that as high loads are applied to the malleable aluminum particles, they deform slightly but do not shatter resulting in an increased bearing area against the formation wall, reducing stress on the malleable aluminum particle and reducing penetration of the malleable aluminum particle into the formation. Kern assesses the performance of nearly spherical aluminum particles which are deformed to produce nearly uniform disks (deformed thickness less than or equal to 0.5 times the original nearly spherical diameter). Kern suggests that malleable aluminum could be used in combination with sand to lower costs (compared to aluminum alone) and to provide a safety net in the event the aluminum does not perform as expected.
Disadvantages of propping with aluminum include limitations associated with the specific gravity of aluminum which restricts the fluids which may be used to place aluminum proppant particles, and the fluid may require special treatment such as viscosification or emulsification, etc., and in addition, as suggested by Kern, the high cost of aluminum is a factor. In addition, formations typically fractured today are very susceptible to damage produced by the fracturing fluid itself. This requires the use of less viscous fluids and physically less liquid (or foam) or gas (nitrogen, carbon dioxide etc.). Less viscous fluids and less volume of liquid or foam or gas means less carrying capacity for proppants, which may mean that proppants may not always enter the fracture or many not be distributed along the full length of the fracture.
U.S. Pat. No. 3,933,205 (Kiel) teaches a method for increasing well productivity by multiple hydraulic fracturing cycles using no proppant (self propping) or using sand as a proppant. The initial cycles are designed to form spalls of the formation material in the fracture and subsequent cycles displace the spalls into the fracture, thus propping the fracture open or creating extensions or branches and propping open the extensions or branches.
However, this method relies on causing formation damage to create the desired spalls and teaches only the use of no proppant or sand as a proppant.
U.S. Pat. No. 5,531,274 (Bienvenu) teaches a high strength, lightweight proppant for use in hydraulic fracturing, having a specific gravity approximately equal to the specific gravity of water. Bienvenu teaches that such a proppant, such as a styrene-divinyl-benzene copolymer bead, set in a formation as a packed mass of particles adjacent to a fracture, will prop open the fracture.
However, when closure stress exceeds the deformation limits of the proppant in the packed mass, the effective permeability of the packed mass (and the related conductivity of the formation) decreases as the proppant is deformed, thus reducing or eliminating the flow channels that normally exist between the particles forming the packed mass.
U.S. Pat. No. 6,059,034 (Rickards et al.) teaches a formation treatment method using deformable particles, the deformable particles formed of a blend of fracture proppant material and deformable particulate. As examples, the fracture proppant material may be a material such as sand, and the deformable particulate may be a material such as polystyrene, as divinylbenzene beads.
However, this blend requires that both materials be blended and sufficiently mixed, and may result in the usual problems with sand type fracturing, such as fines.
It is, therefore, desirable to provide a deformable proppant that avoids the problems of metallic proppants, that is not formed into a deformed packed mass, and can be used on its own without additional proppants to improve stimulation and increase productivity in the fracturing operations of subterranean formations.